Fuel vapor detection system for vehicles

ABSTRACT

An electric motor or generator is used to spin the vehicle&#39;s internal combustion engine while the engine is not running, in order to draw a vacuum within the vapor control system. Vacuum bleed off is then monitored to determine if an unacceptable condition in the control system may exist. The evaporative fuel emissions test may be conducted either while the vehicle is at rest or while under way in an electric drive mode of operation.

FIELD OF THE INVENTION

This invention generally relates to emission control systems forvehicles, and deals more particularly with a method of detectingevaporative fuel emissions for a vehicle.

BACKGROUND OF THE INVENTION

Evaporative emission control systems are well known in internalcombustion engine powered motor vehicles to prevent evaporative fuel,i.e., fuel vapor, from being emitted from the fuel tank into theatmosphere. These control systems typically include several primarycomponents that control evaporative emission operations: vapor controlvalves, vapor management valves and a carbon canister for absorbing thevapors.

From time to time, fuel vapors may be vented improperly, resulting inreduced engine performance and the possibility of vapor emissions intothe atmosphere. A variety of on-board diagnostic systems have beendevised for detecting such emissions in the evaporative emission controlsystem so that appropriate corrective measures may be taken.

Conventional emissions control may include: (1) an intake manifold of anengine connecting to a vapor control system in order to draw a vacuum onthe control system, (2) sealing the vapor control system and/or, (3)bleeding-off and monitoring the resulting vacuum in the control system.With vehicles powered only by an internal combustion engine, these stepscan only be performed while the engine is running. Coordinating therequirements of the engine control system and the evaporative emissioncontrol system test procedure places constraints on both systems.

These problems are exacerbated in hybrid powered vehicles using both aninternal combustion engine and an electric drive motor. Hybrid poweredvehicles, when operating in an internal combustion (IC) mode, tend torun at relatively wide-open throttle for substantial periods in order tomaximize operating efficiency. At open or near wide-open throttle,however, intake manifold pressure is lower, limiting the engine'sability to draw a vacuum in the evaporative emission control system tofacilitate emissions detection.

Accordingly, a need exists in the art for a method of emissionsdetection that can be performed effectively while the engine is notrunning. The present invention is intended to satisfy that need.

SUMMARY OF THE INVENTION

A method is provided for detecting fuel vapor emissions from an internalcombustion engine driven vehicle while the engine is not running. Adetection test can be performed while the vehicle is not operating, orwhile the vehicle is powered by an alternative drive source such as anelectric motor in combination with a battery fuel cell or other electricpower source. In accordance with one embodiment of the present method,the method advantageously uses an onboard electric machine operated in amotor mode, to spin the non-running IC engine in order to draw a vacuumon the vapor emission control system, which is then monitored todiagnose proper operation of the vehicle emissions control system.

In accordance with a first embodiment of the invention, a method isprovided of detecting a fuel vapor emissions of an internal combustion,while the engine is not running. The method includes closing a firstvalve used for controlling the escape of fuel vapor emissions from thesystem, closing a throttle to prevent air from entering the enginethrough the throttle, opening a fuel vapor management valve to connectthe engine with the control system, rotating the engine to reduce thefuel vapor pressure in the control system, then closing the vapormanagement valve and measuring the vapor pressure in the control system,a change in the system pressure indicating a possible unacceptablecondition in the control system. The throttle is closed by moving athrottle plate to a closed position blocking airflow into the intakemanifold of the engine. Rotation of the engine is performed using eitheran electric drive motor or an onboard generator operated as a drivemotor. The detection method may be used in hybrid powered vehicles inwhich the electric drive motor or generator is employed as the powersource to spin the IC engine during the evaporative fuel emissions test.

In accordance with a second embodiment of the invention, a method isprovided for detecting a evaporative fuel emissions in a fuel vaporemission control system of a hybrid powered vehicle having an internalcombustion engine and an electric drive motor. The method comprises thesteps of determining if the IC engine is running, closing the emissioncontrol system when the IC engine is determined not to be running,opening a fuel vapor management valve connecting the engine with theemission control system, rotating the engine to reduce the fuel vaporpressure within the emission control system, closing the fuel vapormanagement valve and then measuring the vapor pressure in the controlsystem to determine whether a evaporative fuel emissions may be present.

These non-limiting features, as well as other advantages of the presentinvention may be better understood by considering the following detailsof a description of a preferred embodiment of the present invention. Inthe course of this description, reference will frequently be made to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a combined block and schematic diagram of a hybrid poweredvehicle provided with a fuel vapor emission control system; and,

FIG. 2 is a flow diagram showing the steps of the method forming thepreferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a vehicle is equipped with an evaporative,fuel vapor emission control system, generally indicated by the numeral10. In the illustrated embodiment, the vehicle is of the hybrid poweredtype, driven by an internal combustion engine 38 and an electric motor50 which drive one or more traction wheels 44 through a set of gears 42.The electric motor 50 is powered by energy stored in a battery 46 whoseDC output is converted to AC by an inverter 48. The electric motor 50may be operated in a regenerative mode to generate electrical power usedfor recharging battery 46. Additionally, an electrical generator 40 alsoproduces electrical energy and is driven either directly by the engine38 or through gear-set 42. Generator 40 may also be operated as anelectric motor capable of spinning (cranking) the IC engine 38 througheither a direct drive connection or via the gear-set 42. The abovementioned drive components are controlled by an electronic enginecontrol (EEC) 34, which also controls the operation of the emissioncontrol system 10.

The emission control system 10 includes a fuel tank 12 having its upperinternal volume in communication with one or more evaporative canisters16 and the intake manifold 14 of engine 38. The fuel tank 12 providesfuel to the engine 38 and typically includes a vapor vent valve 18 aswell as a rollover valve 20. The fuel tank 12 may also include a vacuumrelief valve 22, integral with the fuel tank cap, for preventingexcessive vacuum or pressure from being applied to the fuel tank 12. Thefuel tank 12 further includes a pressure transducer 24 for monitoringfuel tank pressure or vacuum and for providing a corresponding inputsignal to the EEC 34. The pressure transducer 24 may be installeddirectly into the fuel tank 12 or remotely mounted and connected by aline to the fuel tank 12.

Evaporation canister 16 is provided for trapping and subsequently usingfuel vapor dispelled from the fuel tank 12. The evaporation canister 16is connected to the atmosphere through a canister vent valve (CVV) 26. Afilter 28 may be provided between the CVV 26 and the atmosphere forfiltering the air pulled into the evaporation canister 16. The CVV 26may comprise a normally open solenoid controlled by the EEC 34 via anelectrical connection to the CVV 26.

A vapor management valve (VMV) 30 is coupled between the intake manifold14 and a fuel tank 12 and the evaporation canister 16. The VMV 30 maycomprise a normally closed vacuum operated solenoid which is alsoenergized by the EEC 34. When the VMV 30 opens, the vacuum of the intakemanifold 14 draws fuel vapor from the evaporation canister 16 forcombustion in the cylinders of the engine 38. When the EEC 34de-energizes the VMV 30, fuel vapors are stored in the evaporationcanister 16.

The system 10 may further include a service port 32 coupled between theVMV 30 and the fuel tank 12 and the evaporation canister 16. The serviceport 32 aids an operator in performing diagnostics on the emissioncontrol system 10 to identify malfunctions.

In addition to controlling the CVV 26 and VMV 30, the EEC 34 alsocontrols a throttle plate 36 forming part of a throttle body (not shown)which in turn controls the flow of air into the intake manifold 14.

The EEC 34 may perform a series of routine diagnostic tests to determinewhether the emission control system 10 is operating properly, at any ofvarious times when the vehicle is running. These diagnostic tests mayinclude gross evaporative fuel emissions detection and small evaporativefuel emissions detection. In accordance with the method of the presentinvention, however, a diagnostic test to determine the possibility of aevaporative fuel emissions in the control system 10 may be carried outwhile the engine 38 is not running, as would be the case when thevehicle was either being driven under the power of the electric motor 50or when the vehicle is stationary and the IC engine 38 is turned off.

The method of the present invention may be better understood byreferring now also to FIG. 2, which shows the flow chart of the stepscomprising the present method. The evaporative fuel emissions detectionmethod is started at 52 and responds to an initiating signal produced bythe EEC 34 or other on-board controller which initiates periodicdiagnostic tests. A determination is initially made at 54 as to whethera evaporative fuel emissions test needs to be performed based uponcurrent vehicle operating conditions or historical data. For example,pre-programmed instructions may dictate that a evaporative fuelemissions test be performed within ten minutes following turning on ofthe vehicle's ignition. If it is confirmed that a evaporative fuelemissions test is to be initiated, then the existence of a series ofoperating conditions are confirmed at step 56. For example, beforeproceeding with the evaporative fuel emissions test, it must beconfirmed that the pressure within the fuel tank 12 is within aprescribed range, that there have been no sensor or actuator failures,that the tank 12 has not been recently refueled, that the enginecontrols are in a closed loop mode and the vehicle is at idleconditions. Further it is confirmed that the ambient air pressure issufficiently high, that ambient temperature is within a prescribedrange, that the cumulative engine run-time is low enough and that thelevel of the fuel within tank 12 is within a certain range.

Once the conditions in step 56 have been confirmed, a determination ismade at step 58 of whether the IC engine 38 is running. If the engine 38is running, then the EEC 34 initiates a conventional evaporative fuelemissions test of the control system 10. However, if the engine isdetermined not to be running at step 58, then the following steps of themethod of the present invention are carried out to perform evaporativefuel emissions testing.

First, at step 62 a determination is made as to whether the battery 46has a state of charge (SOC) within a prescribed range. If the batterySOC is not within a prescribed range, the process returns to step 54.However, if the battery SOC is within the prescribed range, then theprocess proceeds to step 64 in which both the CVV 26 and the throttleplate 36 are moved to their closed positions. With both the CVV 26 andthrottle plate 36 closed, the emission control system 10 is effectivelyclosed from the atmosphere, since atmospheric air may not pass into thesystem through the CVV 26 and fresh air may not pass into the intakemanifold 14.

Next, at step 66, the VMV 30 is opened, placing the engine 38 in fluidcommunication within the control system 10. Then, at step 68, thegenerator 40 is operated as a motor to spin or “crank” the engine 38,causing the engine's pistons to reciprocate which in turn forces air outof the piston cylinders into an exhaust manifold (not shown). Spinningof the engine 38 therefore reduces the vapor pressure within intakemanifold 14, and thus within the lines and components comprising theemission control system 10. The EEC 34 monitors the vapor pressurewithin the control system 10 and when this pressure drops to apre-selected level representing the necessary vacuum required to performthe evaporative fuel emissions detection, the EEC 34 commands thegenerator 40 to stop spinning the engine 38. If, however, the requisitevacuum level is not created within a pre-selected time period shown instep 72, the evaporative fuel emissions detection method is terminated,and a different protocol is followed, such as the performance of aconventional, gross evaporative fuel emissions detection at step 74.

Assuming however that spinning of the engine 38 reduces the vaporpressure in the control system 10 to the pre-selected level within theprescribed time period, then the VMV 30 is closed at 76 and spinning ofthe engine 38 is terminated at step 78. At this point, with the intakemanifold 14 isolated from the remainder of the control system, the EEC34 monitors the rate of vacuum bleed-off within the control system 10.The rate of vacuum bleed-off, i.e. pressure drop in the control systemis indicative of a possible evaporative fuel emissions in the system. Ifthe pressure drop exceeds a pre-selected rate then a flag is issuedwithin the EEC 34 which records the possibility of a vapor evaporativefuel emissions requiring corrective action.

From the foregoing, it can be seen that the method of the presentinvention provides a very simple evaporative fuel emissions detectionmethod which uses the IC engine 38 to produce a vacuum within theemission control system 10, then seals the control system andsubsequently monitors the ability of the system to maintain this vacuum.When used in a hybrid vehicle, advantage can be taken of the electricdrive motor or generator to spin the IC engine 38 to produce the vacuumwhile the engine is not running. Although a generator 40 has beendisclosed as being the motive means for spinning the IC engine 38, thespinning could also be produced by power from the electric motor 20which is transmitted as a torque through the gear-set 42 to thecrankshaft of the IC engine 38.

It is to be understood that the specific methods and techniques whichhave been described are merely illustrative of one application of theprinciples of the invention. Numerous modifications may be made to themethod and system as described without departing from the true spiritand scope of the invention.

1. A method of detecting evaporative fuel emissions in a fuel vaporemission control system of an internal combustion engine driven vehiclewhile the engine is not running, comprising the steps of: opening a fuelvapor management valve connecting the engine with the control system;rotating the engine to reduce the fuel vapor pressure in the controlsystem; and measuring the vapor pressure in the control system, a changein pressure being related to possible fuel vapor evaporative fuelemissions in the control system.
 2. The method of claim 1 furthercomprising the steps, prior to said opening step, of: closing a firstvalve for controlling the escape of fuel vapor from the control systemto the atmosphere; and closing a throttle on the engine to prevent airfrom entering into the engine through the throttle.
 3. The method ofclaim 2 further comprising the step, inbetween said rotating step andsaid measuring step, of: closing the vapor management valve.
 4. Themethod of claim 2, wherein the step of closing the throttle comprisesclosing a throttle plate controlling the flow of air into engine.
 5. Themethod of claim 1, wherein the step of rotating the engine comprisespowering the engine using an electric drive motor.
 6. The method ofclaim 1, wherein the rotating step is continued for a preselected lengthof time.
 7. The method of claim 6, wherein the step of measuring thevapor pressure is performed continuously during the preselected lengthof time.
 8. The method of claim 6, further comprising the step ofclosing a vapor management after the preselected time period.
 9. Themethod of claim 1, wherein the rotating step is continued for apreselected length of time, and the method further comprises closing avapor management valve when the measured vapor pressure is below apreselected pressure.
 10. The method of claim 1, wherein the rotatingstep comprises powering the engine with an electrical generator operatedas an electric motor.
 11. The method of claim 1, wherein the methodfurther comprises ending rotation of the engine after the vapor pressurehas been measured for a preselected length of time.
 12. The method ofclaim 11, wherein the method further comprises monitoring the vaporpressure after the engine rotation of the engine has ended.
 13. A methodof detecting a evaporative fuel emissions in an evaporative vaporcontrol system for a vehicle having a fuel tank, a vent valvecontrolling the flow of fuel vapor to a vent, an internal combustionengine having an intake manifold and a throttle valve for controllingthe flow of air into the intake manifold, and a vapor management valvefor controlling the flow of fuel vapor between the control system andthe engine, comprising the steps of: closing the vent valve; closing thethrottle valve to prevent air from being drawn into the engine; openingthe vapor management valve to place the intake manifold in fluidcommunication with the control system; rotating the engine using anauxiliary power source to produce a partial vacuum in the controlsystem; closing the vapor management valve; and, measuring changes thevapor pressure within the control system, changes in the vapor pressureindicating a possible evaporative fuel emissions in the control system.14. The method of claim 13, wherein closing the throttle valve comprisesclosing a throttle plate controlling air flow into he intake manifold.15. The method of claim 13, wherein rotating the engine is performed byusing an electrical generator as the auxiliary power source.
 16. Themethod of 13, wherein the rotating step is continued until the vaporpressure within the control system is reduced to a preselected pressurevalue.
 17. A method of claim 13, wherein the rotating step is continuedfor a presented length of time.
 18. The method of claim 13, wherein themethod further comprises stopping rotation of the engine and themeasuring step is performed after the rotating step has stopped.
 19. Amethod of detecting a evaporative fuel emissions in a fuel vaporemission control system of a hybrid powered vehicle having an internalcombustion engine and an electric drive motor, comprising the steps of:determining if the internal combustion engine is running; if theinternal combustion engine is determined not to be running, closing theemission control system; opening a fuel vapor management valveconnecting the engine with the emission control system; rotating theengine to reduce the fuel vapor pressure within emission control system;closing the fuel vapor management valve; and measuring the vaporpressure in the emission control system, a change in the vapor pressureindicating a possible fuel vapor evaporative fuel emissions in theemission control system.
 20. The method of claim 19, wherein closing theemission control system comprises closing a valve connecting theemission control system with the atmosphere.
 21. The method of claim 20,wherein closing the emission control system further comprises closing anengine throttle valve to prevent the flow of air into the engine. 22.The method of claim 19, wherein closing the emission control systemcomprises closing an engine throttle valve to prevent the flow of airinto the engine.
 23. The method of claim 19, wherein rotating the enginecomprises driving the engine with the electric motor.
 24. The method ofclaim 19, wherein rotating the engine comprises driving the engine withan electric generator.
 25. The method of claim 19, wherein rotating theengine is performed for a preselected length of time.
 26. The method ofclaim 19, wherein rotating the engine is performed until the vaporpressure in the emission control system is reduced to a preselectedpressure level.
 27. The method of claim 25, wherein the step ofmeasuring the vapor pressure level is performed after the vapor pressurehas been reduced to at least the preselected pressure level.